1. Field of the Invention
The present invention relates to a color image forming apparatus using an electrophotographic system, such as a laser printer, a copier, or a facsimile.
2. Description of the Related Art
Conventionally, there has been known a configuration of an electrophotographic image forming apparatus including collecting means and a collecting container for collecting an adhering toner that is not transferred onto a transfer material and remaining on an image bearing member (photosensitive drum or intermediate transfer member).
A color image forming apparatus generally uses four colors of toner: Y (yellow), M (magenta), C (cyan), and K (black). For respective color toners, corresponding developing devices (developing roller and developing storage container) are provided. Further, in order to dispense with the collecting container for the photosensitive drum, there has conventionally known a method collecting the adhering toner into the developing device and reusing the collected toner in image formation. However, in the color image forming apparatus, since the respective color toners are superposed one another when forming a color image, there are cases where plurality of color toners are mixed to be adhered on the photosensitive drum. There is a problem in that when those mixed color toners are recollected into the developing storage container of a particular developing device, there causes color mixture within the developing container, which leads to a variation in color tone when an image forming operation is performed to form an image. In particular, when the black color is mixed with yellow, cyan, and magenta colors, respectively, large variation in color tone occurs.
In order to solve this problem, Japanese Patent Application Laid-Open No. 2004-279474 discloses a system in which a mixed-color toner on a transfer member is recollected into a developing storage container of a black developing device. This is based on such characteristics that a black color appears when yellow, cyan, and magenta colors are mixed.
Further, Japanese Patent Application Laid-Open No. 2001-324855 discloses a system in which a patch toner of a single-color toner formed on a transfer member is recollected into a developing storage container of developing device for respective colors.
However, for example, when such a jamming occurs that the transfer material conveyed within the image forming apparatus is stopped in the midway, or when a misprinting occurs, a large amount of toner adheres onto an intermediate transfer belt and a conveying belt.
Note that, the term “jamming” refers to a state in which the image forming operation is aborted due to a conveying failure of the transfer material from a cassette to a fixing device. The term “misprinting” refers to a state in which the image formation is stopped, leaving a toner adhering onto the intermediate transfer belt, due to unmatching between an image size formed on the intermediate transfer belt and a transfer material size, deviation of an image formation timing and conveyance timing of the transfer material, and the like.
A color ratio of those adhering toners is determined depending on a print at the time of printing, and hence it is not able to specify the color ratio. In such state, when the entire toners are recollected into a developing storage container of a black developing device, there is a high possibility of causing a variation in black color tone at the time of image formation.
Further, unlike the patch toner, the toners which have adhered onto the belt due to the jamming, the misprinting, and the like are not formed of a single-color toner. Therefore, it is impossible to recollect the toners into the developing storage container of the developing device for respective colors.